Diy Boat Cup Holder . In this video i repurpose a moulded plastic drink cup holder, and mount it in the boat. The cup holder was mounted onto this. Portable Dual Cup Holder Overtons 44.99 Boat cup holders, Cup from www.pinterest.com Mine was 3” wide, by 3” tall. In this quick video, i overview how i made a simple bracket and cup holder for my grandfather's jon boat. Mounting the cup, cup holder.